Targeted photodestruction of human colon cancer cells using charged 17.1A chlorin e6 immunoconjugates

Chlorin e6: A Promising Photosensitizer in Photo-Based Cancer Nanomedicine

Conventional cancer treatment modalities are often associated with major therapeutic limitations and severe side effects. Photodynamic therapy is a localized noninvasive mode of treatment that has given a different direction to cancer research due to its effectivity against a wide range of cancers and minimal side effects. A photosensitizer is the key component of photodynamic therapy (PDT) that generates cytotoxic reactive oxygen species to eradicate cancer cells. As the therapeutic effectivity of PDT greatly depends upon the photosensitizer, great efforts have been made to search for an ideal photosensitizer. Chlorin e6 is a FDA approved second generation photosensitizer that meets the desired clinical properties for PDT. It is known for its high reactive oxygen species (ROS) generation ability and anticancer potency against many types of cancer. Hydrophobicity is a major drawback of Ce6 that leads to its poor biodistribution and rapid clearance from the circulatory system. To overcome this drawback, researchers have designed and fabricated several types of nanosystems, which can enhance Ce6 solubility and thereby enhance its bioavailability. These nanosystems also improve tumor accumulation of Ce6 by selectively targeting the cancer cells through passive and active targeting. In addition, Ce6 has been employed in many combination therapies like chemo-photodynamic therapy, photoimmunotherapy, and combined photodynamic-photothermal therapy. A combination therapy is more curative than a single therapy due to the synergistic effects of individual therapies. Ce6-based nanosystems for combination therapies have shown excellent results in various studies and provide a promising platform for cancer treatment.

Targeted photoimmunotherapy for cancer

Photodynamic therapy (PDT) is a clinically approved procedure that can exert a curative action against malignant cells. The treatment implies the administration of a photoactive molecular species that, upon absorption of visible or near infrared light, sensitizes the formation of reactive oxygen species. These species are cytotoxic and lead to tumor cell death, damage vasculature, and induce inflammation. Clinical investigations demonstrated that PDT is curative and does not compromise other treatment options. One of the major limitations of the original method was the low selectivity of the photoactive compounds for malignant over healthy tissues. The development of conjugates with antibodies has endowed photosensitizing molecules with targeting capability, so that the compounds are delivered with unprecedented precision to the site of action. Given their fluorescence emission capability, these supramolecular species are intrinsically theranostic agents.

Synthesis and characterization of a reconstituted myoglobin-chlorin e6 adduct for theranostic applications

Chlorin e6 (Ce6) and its derivatives are among the most important photosensitizers in photodynamic therapy. Due to their intense fluorescence, chlorins may also be used for diagnostics. However, low solubility in water and high tendency to aggregation restrict their medical use. Here we demonstrate that apo-myoglobin, by reinserting Ce6 in its heme binding pocket, can be used to monomolecularly disperse it. The reconstructed myoglobin-Ce6 adduct presents noticeable changes in the photophysical properties of the chromophore. A red-shift, in particular in the transparency window, can be observed in the absorption and in the emission spectra of the adduct compared to the spectra of the free chlorin in PBS. The adduct presents a higher quantum yield and an increased excited-state lifetime with respect to the free Ce6. The binding of Ce6 to apo-myoglobin determines a decrease of the 1O2 generation but a three-fold increase of peroxides production, determining globally an increase in the performance of Ce6 as a photosensitizer and imaging agent.

Porphyrins as ligands for 64copper: background and trends

Porphyrins and 64Cu have emerged as a novel synergic option for applications in PET molecular imaging. Both the characteristics and photophysical properties of macrocyclic porphyrins and the relatively long half-life of the copper isotope, in addition to the increased tumor-specific uptake of porphyrins compared to normal cells, make this complex an attractive option not only for diagnosis but also for therapeutic applications. Herein, we present an overview of the latest results on the development of PET agents based on porphyrins and 64Cu, including methods used to improve the selectivity of these macrocycles when conjugated with biological units such as monoclonal antibodies, peptides or proteins.

Targeted Photodynamic Therapy: A Novel Approach to Abolition of Human Cancer Stem Cells

Cancer is a global burden that has prompted extensive research into prevention and treatment, over many decades. Scientific studies have shown that subset of cells within a tumour, known as cancer stem cells (CSCs), are responsible for tumourigenesis, metastasis, drug resistance, and recurrences. CSCs have characteristic features of enhanced self-renewal, proliferation, and limited but multidirectional differentiation capacity. The discovery of CSCs has initiated extensive research into novel cancer treatment regimes. Evidence indicates that CSCs are resistant to conventional chemo- and radiation therapy leading to treatment failures, cancer metastasis, secondary cancer formation, and relapse. Because of the observed phenomena in the course of cancer prognosis, a need for treatment modalities targeting CSCs is important. Photodynamic therapy (PDT) is a clinically approved, minimally invasive, therapeutic procedure that can exert a selective cytotoxic activity toward cancerous cells while reducing toxicity to normal cells. It uses a photosensitizer (PS) that becomes excited when subjected to light at a specific wavelength, and the PS forms reactive oxygen species (ROS) killing malignant cells. Currently, PDT is being investigated as a target specific treatment for CSCs by the addition of carrier molecules and antibody conjugates bound to the PS. Targeted PDT (TPDT) may be able to not only eradicate the tumour mass but kill CSCs as well.

Targeted photodynamic therapy as potential treatment modality for the eradication of colon cancer and colon cancer stem cells

Colorectal cancer is commonly treated by tumour resection, as chemotherapy and radiation have proven to be less effective, especially if the tumour has metastasized. Resistance to therapies occurs in almost all patients with colorectal cancer, especially in those with metastatic tumours. Cancer stem cells have the ability to self-renew, and their slow rate of cycling enhances resistance to treatment and increases the likelihood of tumour recurrence. Most metastatic tumours are unable to be surgically removed, thus creating a need for treatment modalities that target cancers directly and destroy cancer stem cells. Photodynamic therapy involves a photosensitizer that when exposed to a light source of a particular wavelength becomes excited and produces a form of oxygen that kills cancer cells. Photodynamic therapy is currently being investigated as a treatment modality for colorectal cancer, and new studies are exploring enhancing photodynamic therapy efficacy with the aid of drug carriers and immune conjugates. These modifications could prove effective in targeting cancer stem cells that are thought to be resistant to photodynamic therapy. In order for photodynamic therapy to be an effective treatment in colorectal cancer, it requires treatment of both primary tumours and the metastatic secondary disease that is caused by colon cancer stem cells. This review focuses on current photodynamic therapy treatments available for colorectal cancer and highlights proposed actively targeted photosynthetic drug uptake mechanisms specifically mediated towards colon cancer stem cells, as well as identify the gaps in research which need to be investigated in order to develop a combinative targeted photodynamic therapy regime that can effectively control colorectal cancer primary and metastatic tumour growth by eliminating colon cancer stem cells.

Antibodies armed with photosensitizers: from chemical synthesis to photobiological applications

Targeting photosensitizers to cancer cells by conjugating them with specific antibodies, able to recognize and bind to tumor-associated antigens, is today one of the most attractive strategies in photodynamic therapy (PDT). This comprehensive review updates on chemical routes available for the preparation of photo-immunoconjugates (PICs), which show dual chemical and biological functionalities: photo-properties of the photosensitizer and the immunoreactivity of the antibody. Moreover, photobiological results obtained with such photo-immunoconjugates using in vitro and in vivo cancer models are also discussed.

Photodynamic therapy in colorectal cancer treatment--The state of the art in preclinical research

BACKGROUND

Photodynamic therapy (PDT) is used in many different oncologic fields. Also in gastroenterology, where have been a few attempts to treat both the premalignant lesion and advanced colorectal cancer (CRC). This review aims to give a general overview of preclinical photodynamic studies related to CRC cells and animal studies of photodynamic effects related to CRC treatment to emphasize their potential in study of PDT mechanism, safety and efficiency to translate these results into clinical benefit in CRC treatment.

MATERIALS AND METHOD

Literature on in vitro preclinical photodynamic studies related to CRC cells and animal studies of photodynamic effects related to CRC treatment with the fallowing medical subject headings search terms: colorectal cancer, photodynamic therapy, photosensitizer(s), in vitro, cell culture(s), in vivo, animal experiment(s). The articles were selected by their relevance to the topic.

RESULTS

The majority of preclinical studies concerning possibility of PDT application in colon and rectal cancer is focused on phototoxic action of photosensitizers toward cultured colorectal tumor cells in vitro. The purposes of animal experiments are usually elucidation of mechanisms of observed photodynamic effects in scale of organism, estimation of PDT safety and efficiency and translation of these results into clinical benefit.

CONCLUDING REMARKS

In vitro photodynamic studies and animal experiments can be useful for studies of mechanisms and efficiency of photodynamic method as a start point on PDT clinical research. The primary disadvantage of in vitro experiments is a risk of over-interpretation of their results during extrapolation to the entire CRC.

Antibody-based imaging strategies for cancer

Although mainly developed for preclinical research and therapeutic use, antibodies have high antigen specificity, which can be used as a courier to selectively deliver a diagnostic probe or therapeutic agent to cancer. It is generally accepted that the optimal antigen for imaging will depend on both the expression in the tumor relative to normal tissue and the homogeneity of expression throughout the tumor mass and between patients. For the purpose of diagnostic imaging, novel antibodies can be developed to target antigens for disease detection, or current FDA-approved antibodies can be repurposed with the covalent addition of an imaging probe. Reuse of therapeutic antibodies for diagnostic purposes reduces translational costs since the safety profile of the antibody is well defined and the agent is already available under conditions suitable for human use. In this review, we will explore a wide range of antibodies and imaging modalities that are being translated to the clinic for cancer identification and surgical treatment.

Pheophorbide-a conjugates with cancer-targeting moieties for targeted photodynamic cancer therapy

Pheophorbide-a, a non-selective photosensitizer, was conjugated with cancer-targeting moieties, such as folic acid, the CRGDLASLC peptide, the cRGDfK peptide and leuprorelin, for the purpose of targeted photodynamic cancer therapy. The cellular uptake of pheophorbide-a conjugates in cancer cells overexpressing the corresponding receptors of the targeting moieties was largely enhanced compared with that in the receptor-negative cells. In the study of in vitro photodynamic activity and selectivity of pheophorbide-a conjugates in the receptor-positive and receptor-negative cells, a pheophorbide-a conjugate, (14) with an αvβ6 ligand (CRGDLASLC) exhibited the highest selectivity in the positive FaDu cells. Targeted PDT with 14 induced cell death through apoptosis and morphological apoptosis-like characteristics. These results suggest that pheophorbide-a conjugate 14 could be utilized in selective photodynamic therapy for oral cancers primarily expressing the αvβ6 receptor.

Somatostatin analogues for receptor targeted photodynamic therapy

Photodynamic therapy (PDT) is an established treatment modality, used mainly for anticancer therapy that relies on the interaction of photosensitizer, light and oxygen. For the treatment of pathologies in certain anatomical sites, improved targeting of the photosensitizer is necessary to prevent damage to healthy tissue. We report on a novel dual approach of targeted PDT (vascular and cellular targeting) utilizing the expression of neuropeptide somatostatin receptor (sst₂) on tumor and neovascular-endothelial cells. We synthesized two conjugates containing the somatostatin analogue [Tyr3]-octreotate and Chlorin e6 (Ce6): Ce6-K₃-[Tyr3]-octreotate (1) and Ce6-[Tyr3]-octreotate-K₃-[Tyr3]-octreotate (2). Investigation of the uptake and photodynamic activity of conjugates in-vitro in human erythroleukemic K562 cells showed that conjugation of [Tyr3]-octreotate with Ce6 in conjugate 1 enhances uptake (by a factor 2) in cells over-expressing sst₂ compared to wild-type cells. Co-treatment with excess free Octreotide abrogated the phototoxicity of conjugate 1 indicative of a specific sst₂-mediated effect. In contrast conjugate 2 showed no receptor-mediated effect due to its high hydrophobicity. When compared with un-conjugated Ce6, the PDT activity of conjugate 1 was lower. However, it showed higher photostability which may compensate for its lower phototoxicity. Intra-vital fluorescence pharmacokinetic studies of conjugate 1 in rat skin-fold observation chambers transplanted with sst₂⁺ AR42J acinar pancreas tumors showed significantly different uptake profiles compared to free Ce6. Co-treatment with free Octreotide significantly reduced conjugate uptake in tumor tissue (by a factor 4) as well as in the chamber neo-vasculature. These results show that conjugate 1 might have potential as an in-vivo sst₂ targeting photosensitizer conjugate.

Synthesis and biological investigations of a ZnPc-antiCEA bioconjugate for imaging of colorectal cancer

Two zinc(II) phthalocyanines (ZnPcs) were conjugated with a monoclonal antibody (MAb) directed against carcinoembryonic antigen (CEA), using an in situ activated carboxylic acid on the ZnPcs. The bioconjugate with the highest ZnPc/MAb ratio of 3 was investigated in vitro for its ability to target and fluorescently label human colorectal HT-29 cells. The ZnPc-CEA MAb 2 was observed to efficiently target HT-29 cells, about 37 times more than unconjugated ZnPc. Furthermore, in the presence of a 4-fold excess of unlabelled anti-CEA antibody, the fluorescence signal of 2 was reduced by ~90% showing that the targeting is CEA-mediated. These studies further confirm the high specificity of Pc-antibody conjugates for antigens over-expressed on tumor cells and warrant further investigations of these immunoconjugates and their derivatives for imaging of colorectal cancer.

Photoimmunotherapy and irradiance modulation reduce chemotherapy cycles and toxicity in a murine model for ovarian carcinomatosis: perspective and results

Significant toxicities from multiple cycles of chemotherapy often cause delays or early termination of treatment, leading to poor outcomes in ovarian cancer patients. Complementary modalities that potentiate the efficacy of traditional agents with fewer cycles and less toxicity are needed. Photodynamic therapy is a mechanistically-distinct modality that synergizes with chemo and biologic agents. A combination regimen with a clinically relevant chemotherapy cocktail (cisplatin + paclitaxel) and anti-EGFR targeted photoimmunotherapy (PIT) is evaluated in a murine model for ovarian carcinomatosis. Mice received either 1 or 2 chemotherapy cycles followed by PIT with a chlorine6-Erbitux photoimmunoconjugate and 25 J/cm2 light. PIT + 1 cycle of chemotherapy significantly reduced tumor burden, comparable to multiple chemotherapy cycles. Relative to 1 cycle of chemotherapy, the addition of PIT did not cause significant mouse weight loss, whereas 2 cycles of chemotherapy led to a significant reduction in weight. Irradiance-dependence on PIT efficacy was a function of the conjugation chemistry, providing an additional variable for optimization of PIT outcome.

Characterization of a conjugate between Rose Bengal and chitosan for targeted antibiofilm and tissue stabilization effects as a potential treatment of infected dentin

Bacterial biofilms and dentin structural changes are some of the major challenges in the management of infected dentin tissue. This study characterized a photosensitizer-conjugated chitosan with enhanced photodynamic efficacy against dental biofilms, as well as the ability to reinforce the postinfected dentin matrix in order to improve its mechanical and chemical stability. Rose Bengal-conjugated chitosan (CSRB) was synthesized using a chemical cross-linking method and characterized for photophysical, photobiological, and cytotoxicity properties. Its potential as an antibacterial and matrix-reinforcing agent on dentin collagen was also evaluated. Enterococcus faecalis as planktonic and in vitro biofilms was treated with CSRB and photodynamically activated with 5 to 60 J/cm(2) green light. Dentin collagen was used for the CSRB cross-linking experiments and evaluated for chemical changes, resistance to enzymatic degradation, and mechanical properties. CSRB was a photosensitizer with efficient singlet oxygen yield. In vitro photoactivation gave higher fibroblast cell survival than did RB alone. CSRB showed significant antibiofilm photoinactivation (P < 0.01). The CSRB-cross-linked dentin collagen showed higher resistance to collagenase degradation and superior mechanical properties (P < 0.05). In summary, the photoactivated CSRB particles synthesized in this study may be a synergistic multifunctional treatment approach with lower cytotoxicity and effective antibiofilm activity as well as the ability to reinforce the dentin collagen to enhance resistance to degradation and improve mechanical properties. This may be a targeted treatment strategy to deal with infected dentin hard tissues in a clinical scenario, where both disinfection and structural integrity need to be addressed concomitantly.

Strategies for selective delivery of photodynamic sensitisers to biological targets

Strategies for increasing the affinity of photodynamic sensitisers for specific tissues, cells and organisms are reviewed. Biological outcomes are evaluated and therapeutic potential assessed.

Preparation of chlorin e6–monoclonal antibody conjugate and its effect for photodynamic therapy

Chlorin e6 ( Ce 6) was conjugated with anti-tumor monoclonal antibody ( IgG 2 b ) to increase its binding affinity for tumors. The Ce 6 was activated by N -hydroxysuccinimide and directly conjugated with IgG 2 b ( IgG 2 b – Ce 6) via peptide bonds. An average of 11 Ce 6 molecules were coupled to each IgG2b molecule. IgG 2 b – Ce 6 showed high cellular uptake in tumor cells and high photocytotoxicity. These results indicate IgG 2 b – Ce 6 is a good photosensitizer with high binding affinity to tumor cells.

Cellular localization and photodynamic effect of chlorine6-monoclonal antibody conjugate

Chlorin e6(Ce6) was conjugated with anti-tumor monoclonal antibody ( IgG ) to increase its binding affinity for tumors. Ce 6 was activated by N -hydroxysulfosuccinimide and conjugated with IgG via peptide bonds, and Ce 6 molecules were conjugated with IgG ( IgG - Ce 6) and their binding affinities to tumor cells were investigated. Intracellular localization of IgG - Ce 6 was observed, and IgG - Ce 6 was accumulated in tumor cells much higher than Ce 6, indicating that the IgG - Ce 6 has specific binding affinity to tumor cells. The effective photocytotoxicity of the cells with IgG - Ce 6 is caused by the high accumulation of IgG - Ce 6 in tumor cells.

Mechanisms of porphyrinoid localization in tumors

The photosensitizing and pharmacokinetic properties of porphyrin-type compounds have been investigated for nearly a century. In the last decade, two porphyrin derivatives were approved in the U.S.A. and in several other countries for the photodynamic treatment of various lesions. An overview of the different mechanisms for preferential porphyrinoid localization in malignant tumors is presented herein. Several uptake pathways are possible for each photosensitizer, which are determined by its structure, mode of delivery and tumor type. Comparisons of the different mechanisms and correlations with the structure of the sensitizer are presented. Current delivery systems for porphyrin sensitizers are described, as well as recent strategies for enhancing their tumor-specificity, including conjugation to a carrier system that selectively targets a tumor-associated receptor or antigen.

Synthesis of porphyrin-carbohydrate conjugates using "click" chemistry and their preliminary evaluation in human HEp2 cells

Using a Cu ( I )-catalyzed carbohydrate azide-alkynylphenylporphyrin cycloaddition (the so-called "click" chemistry), we have synthesized in high yields, a series of four new porphyrin-carbohydrate conjugates containing either one or four galactose or lactose moieties linked via triazole units to a meso-phenyl group of a TPP or tetrabenzoporphyrin (TBP) macrocycle. The time-dependent uptake and subcellular distribution of this series of porphyrin-carbohydrate conjugates were evaluated in human carcinoma HEp2 cells. While the three TPP conjugates accumulated to a similar extent within cells and localized mainly in the ER and endosomes, the TBP-galactose conju gate was the one most efficiently taken up by the HEp2 cells, accumulating approximately 5 times more than the TPP conjugates, and localized preferentially within the cell lysosomes.

Design of photosensitizer/cyclodextrin nanoassemblies: spectroscopy, intracellular delivery and photodamage

The engineering of multifunctional nanoparticles carrying photosensitizer drugs (PS) and exposing binding groups for cellular receptors is of increasing interest in therapeutics and diagnostics applications. Natural and modified cyclodextrins (CDs) offer useful scaffolds to bind PS guests by supramolecular interactions. In particular, amphiphilic β-CDs, which form nanoaggregates of diverse shape and size according to the polarity of substituent groups on the rims, include in their different compartments as CD cavity, hydrophilic and hydrophobic portion, PS with different physicochemical properties. PS embedded in cationic amphiphilic CD nanoassemblies are effective in inducing photodynamic damage in cancer cells. For a carrier/PS system to be used in photodynamic therapy (PDT) or photodynamic diagnosis (PDD), the appropriate combination of the delivery characteristics with the preservation of the photodynamic activity of the PS is strictly required. Homogeneous multilayer films based on cationic amphiphilic β-CD entrapping anionic porphyrins can be constructed to exploit interfacial electrostatic interactions between the two components. The capability of CDs to generate restricted microenvironments for PS which can facilitate photoinduced energy transfer with suitable donor molecules was investigated for potential application in fluorescence diagnosis. Besides, recent findings suggest that PDT could represent a useful tool for properly addressing an alternative approach for killing pathogens and combating infections at a clinical level. Finally, modified CDs can bind gold nanoparticles, yielding hybrid organic/inorganic nanoparticles which were studied in water solution and after casting on solid substrates. These binary assemblies could further encapsulate PS or other conventional drugs, opening new intriguing routes on multimodal therapy.

Targeting of T/Tn antigens with a plant lectin to kill human leukemia cells by photochemotherapy

Photochemotherapy is used both for solid tumors and in extracorporeal treatment of various hematologic disorders. Nevertheless, its development in oncology remains limited, because of the low selectivity of photosensitizers (PS) towards human tumor cells. To enhance PS efficiency, we recently covalently linked a porphyrin (TrMPyP) to a plant lectin (Morniga G), known to recognize with high affinity tumor-associated T and Tn antigens. The conjugation allowed a quick uptake of PS by Tn-positive Jurkat leukemia cells and efficient PS-induced phototoxicity. The present study was performed: (i) to evaluate the targeting potential of the conjugate towards tumor and normal cells and its phototoxicity on various leukemia cells, (ii) to investigate the mechanism of conjugate-mediated cell death. The conjugate: (i) strongly increased (×1000) the PS phototoxicity towards leukemic Jurkat T cells through an O-glycan-dependent process; (ii) specifically purged tumor cells from a 1∶1 mixture of Jurkat leukemia (Tn-positive) and healthy (Tn-negative) lymphocytes, preserving the activation potential of healthy lymphocytes; (iii) was effective against various leukemic cell lines with distinct phenotypes, as well as fresh human primary acute and chronic lymphoid leukemia cells; (iv) induced mostly a caspase-independent cell death, which might be an advantage as tumor cells often resist caspase-dependent cell death. Altogether, the present observations suggest that conjugation with plant lectins can allow targeting of photosensitizers towards aberrant glycosylation of tumor cells, e.g. to purge leukemia cells from blood and to preserve the normal leukocytes in extracorporeal photochemotherapy.

Morniga G: a plant lectin as an endocytic ligand for photosensitizer molecule targeting toward tumor-associated T/Tn antigens

Porphyrins are used as photosensitizer (PS) in photodynamic therapy in cancer treatment. Nevertheless, the development of photochemotherapy in oncology remains limited, because of the low selectivity of PSs. In order to allow PS targeting toward tumor-associated antigens, for the first time a white-light activatable porphyrin, [5-(4-(5-carboxy-1-butoxy)-phenyl)-10,15,20-tris(4-N-methyl)-pyridiniumyl)-porphyrin] (TrMPyP) was covalently linked to Morniga G (MorG), a galactose-specific binding plant lectin, known to recognize with high-affinity tumor-associated T/Tn antigen in cell-free systems. Firstly, using fluorescein-labeled MorG, the sugar-dependent binding and uptake of lectin by Tn-positive (Jurkat lymphoid leukemia) cells was demonstrated. Secondly, the TrMPyP-MorG conjugate was molecularly characterized. Cytometric and confocal microscopic analysis demonstrated that PS covalent linking to MorG preserved sugar-dependent specific binding and uptake of lectin by Jurkat leukemia lymphocytes. Thirdly, the conjugate (with a 1:1 PS:lectin ratio) that was bound and quickly (5 min) taken-up, induced greater than 90% cytotoxicity upon irradiation at 10 nm concentration, whereas the free PS was absolutely nontoxic. On the contrary, normal lymphocytes strongly resisted to the conjugate-mediated phototoxicity. Thus, owing to their binding and endocytosis capacities, plant lectins represent promising molecules for targeting of tumor glycan alteration and to enhance the efficiency of specific delivery of PSs to tumor cells.

FTIR spectra and normal-mode analysis of chlorin e(6) and its degradation-induced impurities

Fourier transform infrared spectra of chlorin e(6) and its trisodium salt are presented. The geometrical structure and frequencies of normal vibrations of both compounds were calculated using density functional method with the PBE exchange-correlation functional. The frequencies were assigned and IR spectra of the studied molecules were interpreted for the first time. Spectral effects of degradation of chlorin e(6) and its trisodium salt upon their storage on the air are analyzed. The possible structures of degraded species are discussed.

Selective and effective killing of angiogenic vascular endothelial cells and cancer cells by targeting tissue factor using a factor VII-targeted photodynamic therapy for breast cancer

The cell surface receptor tissue factor (TF) is regarded as a common but specific target on angiogenic tumor vascular endothelial cells (VECs) and tumor cells in many types of cancer including breast cancer. The purpose of this study is to develop a selective and effective TF-targeting photodynamic therapy (PDT) by using its natural ligand factor VII (fVII)-conjugated Sn(IV) chlorin e6 (SnCe6) for the treatment of breast cancer. A cross linker EDC was used to covalently conjugate fVII protein to SnCe6, and the binding activity and phototoxicity was confirmed by ELISA and in vitro PDT. The efficacy of fVII-tPDT was assessed in vitro by crystal violet staining assay and in vivo by measuring tumor size in mice carrying murine or human breast cancer xenografts. We show that active site-mutated (K341A) fVII protein can be internalized into breast cancer cells and vascular endothelial growth factor (VEGF)-stimulated human umbilical vein endothelial cells (HUVECs) as angiogenic VECs. fVII-tPDT not only enhances 12-fold the in vitro efficacy but also selectively and effectively kills angiogenic HUVECs and breast cancer cells via specifically binding of fVII to TF and inducing apoptosis and necrosis as the underlying mechanism. Furthermore, fVII-tPDT can significantly inhibit the tumor growth of murine and human breast cancer without obvious toxicities in mice. We conclude that fVII-tPDT using fVII-SnCe6 conjugate can selectively and effectively kill angiogenic VECs and breast cancer cells in vitro and significantly inhibit the tumor growth of murine and human breast cancer in mice.

Cell specific aptamer-photosensitizer conjugates as a molecular tool in photodynamic therapy

This paper describes the application of a molecular construct of a photosensitizer and an aptamer for photo-therapeutically targeting tumor cells. The key step in increasing selectivity in chemotherapeutic drugs is to create effective molecular platforms that could target cancer cells but not normal cells. Recently, we have developed a strategy via cell-SELEX (Systematic Evolution of Ligands by Exponential Enrichment) to obtain cell specific aptamers using intact viable cells as targets to select aptamers that can recognize cell membrane proteins with high selectivity and excellent affinity. We have identified an aptamer TD05 that only recognizes Ramos cells, a Burkitt’s lymphoma cell line. Here, the high specificity of aptamers in target cell binding and an efficient phototherapy reagent, Ce6, are molecularly engineered to construct a highly selective Aptamer-photosensitizer conjugates (APS) to effectively destroy target cancer cells. Introduction of the APS conjugates followed by irradiation of light selectively destroyed target Ramos cells but not acute lymphoblastic leukemia and myeloid leukemia cell lines. This study demonstrates that the use of cancer specific aptamers conjugated to a photosensitizer will enhance the selectivity of photodynamic therapy. Coupled with the advantages of the cell-SELEX in generating multiple effective aptamers for diseased cell recognition, we will be able to develop highly efficient photosensitizer based therapeutical reagents for clinical applications.

Control and Selectivity of Photosensitized Singlet Oxygen Production: Challenges in Complex Biological Systems

Singlet molecular oxygen is a reactive oxygen species that plays an important role in a number of biological processes, both as a signalling agent and as an intermediate involved in oxidative degradation reactions. Singlet oxygen is commonly generated by the so-called photosensitization process wherein a light-absorbing molecule, the sensitizer, transfers its energy of excitation to ground-state oxygen to make singlet oxygen. This process forms the basis of photodynamic therapy, for example, where light, a sensitizer, and oxygen are used to initiate cell death and ultimately destroy undesired tissue. Although the photosensitized production of singlet oxygen has been studied and used in biologically pertinent systems for years, the photoinitiated behaviour is often indiscriminate and difficult to control. In this Concept, we discuss new ideas and results in which spatial and temporal control of photosensitized singlet oxygen production can be implemented through the incorporation of the sensitizer into a conjugate system that selectively responds to certain triggers or stimuli.

Synthesis and cellular studies of PEG-functionalized meso-tetraphenylporphyrins

The total syntheses of four PEG-functionalized porphyrins, containing one to four low molecular weight PEG chains linked via amide bonds to the para-phenyl positions of meso-tetraphenylporphyrin, are reported. The hydrophobic character of the PEG-porphyrins decreases with the number of PEG chains linked to the porphyrin ring, while their tendency for aggregation in buffered aqueous solution increases. The porphyrins containing one or two PEG chains accumulated within human HEp2 cells to a much higher extent than those having three or four PEGs at the macrocycle periphery. All PEG-porphyrins were found to be non-toxic in the dark, and only those containing one or two PEG chains were phototoxic (IC(50)=2 microM at 1J/cm(2) light dose). The preferential sites of subcellular localization of the porphyrins containing one or two PEG chains were found to be the mitochondria and endoplasmic reticulum (ER), while those containing three or four PEG chains localize preferentially in the lysosomes.

Uses of photodynamic therapy in premalignant and malignant lesions of the gastrointestinal tract beyond the esophagus

Much has recently been written regarding the use of photodynamic therapy for the treatment of esophageal carcinoma and dysplastic Barrett's esophagus. This review, however, describes the clinical experience using photodynamic therapy with various photosensitizer agents for the treatment of diseases in other areas of the gut, especially the pancreaticobiliary tract where European studies have established the role of porfimer sodium photodynamic therapy in the management of patients with cholangiocarcinoma.

The development and characterisation of porphyrin isothiocyanate-monoclonal antibody conjugates for photoimmunotherapy

A promising approach to increase the specificity of photosensitisers used in photodynamic therapy has been through conjugation to monoclonal antibodies (MAb) directed against tumour-associated antigens. Many of the conjugations performed to date have relied on the activated ester method, which can lead to impure conjugate preparations and antibody crosslinking. Here, we report the development of photosensitiser–MAb conjugates utilising two porphyrin isothiocyanates. The presence of a single reactive isothiocyanate allowed facile conjugation to MAb FSP 77 and 17.1A directed against internalising antigens, and MAb 35A7 that binds to a non-internalising antigen. The photosensitiser–MAb conjugates substituted with 1–3 mol of photosensitiser were characterised in vitro. No appreciable loss of immunoreactivity was observed and binding specificity was comparable to that of the unconjugated MAb. Substitution with photosensitiser had a minimal effect on antibody biodistribution in vivo for the majority of the conjugates, although a decreased serum half-life was observed using a cationic photosensitiser at the higher loading ratios. Tumour-to-normal tissue ratios as high as 33.5 were observed using MAb 35A7 conjugates. The internalising conjugate showed a higher level of phototoxicity as compared with the non-internalising reagent, using a cell line engineered to express both target antigens. These data demonstrate the applicability of the isothiocyanate group for the development of high-quality conjugates, and the use of internalising MAb to significantly increase the photodynamic efficiency of conjugates during photoimmunotherapy.

Pegylation of charged polymer-photosensitiser conjugates: effects on photodynamic efficacy

Conjugates between photosensitisers (PS) and charged polymeric carriers are under investigation for photodynamic therapy of cancer and may allow targeting to certain cell types or compartments in tumours. Covalent attachment of polyethylene glycol to macromolecules (pegylation) may alter their pharmacokinetics, cell type targeting, and photophysical properties. Macrophages may take up large amounts of aggregated PS, thus lessening the selectivity for cancer cells in tumours. We investigated the effect of pegylation on the uptake and phototoxicity of poly-L-lysine chlorin(e6) conjugates with either cationic or anionic charges in two cell lines, human ovarian cancer cells and mouse macrophages. The cationic conjugate after pegylation became less aggregated, consumed less oxygen and had reduced cellular uptake. However, the phototoxicity corrected for cellular uptake increased three- to five-fold. In contrast, the anionic succinylated conjugate on pegylation became more aggregated, consumed similar amounts of oxygen, and had higher cellular uptake. The anionic conjugate showed the highest relative phototoxicity towards both the cell lines (compared to the other three conjugates) and it decreased most towards the macrophages after pegylation. Pegylation reduced the amount of oxygen consumed per chlorin(e6) molecule when photosensitised cells were illuminated. These in vitro studies suggest that pegylation alters the phototoxicity of PS conjugates depending on the effect produced on the aggregation state.

Delivery of ribosome-inactivating protein toxin into cancer cells with shock waves

We report on the use of shock waves delivered by a shock-tube to permeabilize cancer cells and potentiate the cytotoxicity of the type-1 ribosome-inactivating protein, saporin. We studied human colorectal cancer HT29 and ovarian cancer OVCAR-5 cells, and used two different cytotoxicity assays, colony formation and loss of mitochondrial activity. A single shock wave and saporin (10(-9) M) produced significant toxicity not seen with either shock wave or drug alone. Increasing the number of shock waves up to five further increased cytotoxicity. Higher toxicity was seen with the clonogenic assay compared to MTT assay. Shock waves may have applications in promoting cytoplasmic delivery of toxins into cancer cells after intratumoral injection.

Effects of photoproducts on the binding properties of protoporphyrin IX to proteins

Photosensitisers are the photoactive molecules used in photodynamic therapy (PDT) of cancer. Despite the importance of their interaction with polypeptides, only the binding to plasma proteins has been investigated in some detail. In our study we compared the binding of Protoporphyrin IX (a clinically useful photosensitiser) to an immunoglobulin G, with the binding to albumins. Binding to IgG is relevant because a possible method of increasing tumour specificity of photosensitisers is to bind them to tumour-specific antibodies. Binding constants to albumins and the immunoglobulin were comparable ( congruent with6 x 10(-6) M(-1)). The apparent number of PPIX molecules bound to each protein was also within a similar range (from 4 to 7). The absence of a shift in the emission spectrum of PPIX bound to IgG, however, indicates that either larger aggregates of PPIX bind to the immunoglobulin or that the binding site leaves PPIX exposed to the buffer. We observed that PPIX photoproducts compete with PPIX for the same binding sites. The number of PPIX molecules bound to each protein in the presence of photoproducts decreased by 50-80%. Due to the spectral overlap between PPIX and its photoproducts, the binding in the presence of photoproducts was investigated using Derivative Synchronous Fluorescence Spectroscopy (DSFS) to improve the spectral separation between chromophores in solution. We also concluded that fluorescence measurements underestimate the number of PPIX molecules binding each protein. In fact, non-linear Scatchard plots (in the case of albumin binding) by definition yield a minimum number of molecules attached to a protein. Moreover, the binding of large aggregates, formed by an unknown number of PPIX molecules, to IgG results in the underestimate of the number of molecules bound. The number of PPIX molecules bound to these proteins is also much larger than the number of sites estimated by protein fluorescence quenching.

State of the art in the delivery of photosensitizers for photodynamic therapy

In photodynamic therapy, one of the problems limiting the use of many photosensitizers (PS) is the difficulty in preparing pharmaceutical formulations that enable their parenteral administration. Due to their low water solubility, the hydrophobic PS cannot be simply injected intravenously. Different strategies, including polymer-PS conjugation or encapsulation of the drug in colloidal carriers such as oil-dispersions, liposomes and polymeric particles, have been investigated. Although these colloidal carriers tend to accumulate selectively in tumour tissues, they are rapidly taken up by the mononuclear phagocytic system. In order to reduce this undesirable uptake by phagocytic cells, long-circulating carriers that consist of surface modified carriers have been developed. Moreover, considerable effort has been directed towards using other types of carriers to improve tumour targeting and to minimize the side effects. One of the approaches is to entrap PS into the lipophilic core of low-density lipoproteins (LDL) without altering their biological properties. The LDL receptor pathway is an important factor in the selective accumulation of PS in tumour tissue owing to the increased number of LDL receptors on the proliferating cell surface. Specific targeting can also be achieved by binding of monoclonal antibodies or specific tumour-seeking molecules to PS or by the coating of PS loaded carriers.

Internalisation enhances photo-induced cytotoxicity of monoclonal antibody-phthalocyanine conjugates

Immunophototherapy of cancer combines the specificity of a monoclonal antibody (MAb) to an overexpressed tumor marker with the phototoxic properties of the conjugated dye. To analyze the potential role of internalisation of the dye on photo-induced cytotoxicity, we compared two target antigens, carcinoembryonic antigen (CEA) that does not internalise and ErbB2 that does. Human ovarian carcinoma SKOv3 cells that express a high level of ErbB2 were transfected with the CEA cDNA. Using FACS analysis, the resulting cell line, SKOv3-CEA-1B9, demonstrated comparable levels of expression of the two target antigens. Aluminium tetrasulfophthalocyanine (AlPcS(4)) was covalently coupled to anti-CEA MAb 35A7, anti-ErbB2 MAb FSP77 and a non-specific MAb PX, via a five-carbon sulfonamide spacer chain (A(1)) at molar ratios ranging from 6 to 9 moles of AlPcS(4) per mole of MAb. The 35A7-(AlPcS(4)A(1))(8) conjugate induced 68% growth inhibition of the SKOv3-CEA-1B9 cell line after a 20 h incubation at 2.50 microg/ml (based on AlPcS(4)A(1) content) following light exposure. However, the FSP77-(AlPcS(4)A(1))(6) conjugate gave a 51% growth inhibition for an AlPcS(4)A(1) concentration as low as 0.04 microg/ml after the same incubation time and exposure to the same light dose. At a 1.25 microg/ml AlPcS(4)A(1) concentration, the FSP77-(AlPcS(4)A(1))(6) conjugate gave a 67% growth inhibition after an incubation time as short as 1 h, reaching a 96% inhibition after an 8 h incubation time. Using an unique cell line that expresses two different target antigens, we demonstrated a clear advantage of an internalising over a non-internalising MAb-dye conjugate in terms of phototoxic efficacy. In vivo evaluation of the photodynamic properties of the conjugates is in progress.

Biodistribution of charged 17.1A photoimmunoconjugates in a murine model of hepatic metastasis of colorectal cancer

Optimizing photodynamic therapy involves attempting to increase both the absolute tumour content of photosensitizer and the selectivity between tumour and surrounding normal tissue. One reason why photodynamic therapy has not been considered suitable for treatment of metastatic tumours in the liver, is the poor selectivity of conventional photosensitizers for tumour compared to normal liver. This report details an alternative approach to increasing this selectivity by the use of antibody-targeted photosensitizers (or photoimmunoconjugates) to target intrahepatic tumours caused by human colorectal cancer cells in the nude mouse, and explores the role of molecular charge on the tumour-targeting efficiency of macromolecules. The murine monoclonal antibody 17.1A (which recognizes an antigen expressed on HT 29 cells) was used to prepare site-specific photoimmunoconjugates with the photosensitizer chlorine6. The conjugates had either a predominant cationic or anionic charge and were injected i.v. into tumour-bearing mice. Biodistribution 3 or 24 h later was measured by extraction of tissue samples and quantitation of chlorine6 content by fluorescence spectroscopy. The photoimmunoconjugates were compared to the polylysine conjugates in an attempt to define the effect of molecular charge as well as antibody targeting. The anionic 17.1A conjugate delivered more than twice as much photosensitizer to the tumour at 3 h than other species (5 times more than the cationic 17. 1A conjugate) and had a tumour:normal liver ratio of 2.5. Tumour-to-liver ratios were greater than one for most compounds at 3 h but declined at 24 h. Tumour-to-skin ratios were high (> 38) for all conjugates but not for free chlorine6. Cationic species had a high uptake in the lungs compared to anionic species. The photoimmunoconjugates show an advantage over literature reports of other photosensitizers, which can result in tumour:normal liver ratios of less than 1.

Scavenger-receptor targeted photodynamic therapy

Covalent conjugation of a photosensitizer to a ligand that specifically recognized and internalized by a cell-surface receptor may be a way of improving the selectivity of photodynamic therapy (PDT). The class A Type-I scavenger receptor of macrophages, which among other ligands recognizes maleylated serum albumin and has a high capacity is a good candidate for testing this approach. Chlorin(e6) was covalently attached to bovine serum albumin to give conjugates with molar substitution ratios of 1:1 and 3:1 (dye to protein), and these conjugates could then be further modified by maleylation. A novel way of purifying the conjugates by acetone precipitation was developed in order to remove traces of unbound dye that could not be accomplished by size-exclusion chromatography. Conjugates were characterized by polyacrylamide gel electrophoresis and thin-layer chromatography. Photosensitizer uptake was measured by target J774 murine macrophage-like cells and nontarget OVCAR-5 human ovarian cancer cells, and phototoxicity was examined after illumination by a 660 nm diode laser by a tetrazolium assay. All of the purified conjugates were taken up by and after illumination killed J774 cells while there was only small uptake and no phototoxicity toward OVCAR-5 cells. The higher dye:protein ratio and maleylation of the conjugates both produced higher uptakes and lower survival ratios in J774 cells. The uptake and phototoxicity by J774 cells were decreased after incubation at 4 degrees C demonstrating internalization, and confocal microscopy with organelle-specific green fluorescent probes showed largely lysosomal localization. Uptake and phototoxicity by J774 cells could both be competed by addition of the scavenger receptor ligand maleylated albumin. These data show that scavenger receptor-targeted PDT gives a high degree of specificity toward macrophages and may have applications in the treatment of tumors and atherosclerosis.